This invention relates to a two-battery power supply system for vehicles.
A prior-art power supply system for vehicles has been as shown in FIG. 1. In the figure, numeral 1 designates an armature coil for generating three phase alternating current, numeral 2 a field coil which is disposed in opposition to the armature coil 1, numeral 3 a rectifier which converts the A.C. output of the armature coil 1 into a direct current, numeral 4 a voltage regulator which regulates the voltage generated by the armature coil 1 to be constant by controlling the current flowing through the field coil 2, numeral 5 a key switch, numeral 6 a battery, numeral 7 a starting motor, numeral 8 an electric load, numeral 9 an ignitor, and numeral 10 an ignition coil.
The operation of the power supply system having the above arrangement will be described herebelow:
When the key switch 5 is closed, current flows through the primary side of the ignition coil 10. Subsequently, an engine, not shown, is rotated by the starting motor 7. Then, the ignitor 9 operates to generate a high voltage on the secondary side of the ignition coil 10. The high voltage is supplied to ignition plugs, not shown, and a mixture in cylinders, not shown, ignites to start the engine. In addition, when the engine starts, the armature coil 1 produces the A.C. output, which is converted into the direct current by the rectifier 3. With the terminal voltage held constant by controlling the current of the field coil 2 by means of the voltage regulator 4, electric power is supplied to the battery 6 as well as the electric load 8 and the ignitor 9 as well as the ignition coil 10.
Since the prior-art system is constructed as described above, the terminal voltage of the battery lowers during the starting of the engine (particularly during cold periods) due to a large current flowing through the starting motor. This leads to the disadvantage that the design of the ignitor and ignition coil inevitably becomes complicated in order to operate the system in spite of great voltage fluctuations (for example, 6 V to 16 V). Further, since the circuit comprises a single battery, the system must be designed so as to withstand surge voltages, etc., at the interruption of the electrical load.